After having fixed a sudo user (and confirm it works!), please also disable PermitRootLogin by setting it to 'no'.

Restart ssh after editing sshd_conf.

If you're squeemish, run dropbear on another port so you can log into your machine in case you made a boo-boo configuring openssh.

Also, more resources for security settings:

https://benchmarks.cisecurity.org/downloads/multiform/index....